Читать книгу The Esophagus - Группа авторов - Страница 241

One of the major limitations of MII–pH is that it only provides a 24‐hour snapshot of a disease process that is chronic in nature, and so it fails to account for day‐to‐day variability of reflux [50]. Patients with GERD or eosinophilic esophagitis (EoE) have dilations of intercellular space (DIS) between esophageal epithelial cells, which are regulated by tight junction proteins. DISs are filled with electrolyte‐rich fluid, a good conductor of electrical current, leading to a low‐impedance signal [51–56, 67]. The degree of DIS is shown to inversely correlate with MI measurements in adult [68] and pediatric [69] populations, showing that MI could serve as a surrogate marker of histological changes in these patients. Consequently, the assessment of persistently impaired mucosal integrity associated with non‐erosive mucosal damage may provide a better surrogate for the evaluation of GERD. Lower baseline intraluminal impedance among patients with esophagitis and NERD has been demonstrated in observational studies. In a study of 35 GERD patients and 17 functional heartburn patients, mucosal impedance was measured during MII–pH testing at night during a period of at least 30 min with a stable baseline activity. Baseline impedance in GERD patients was lower than in those with functional heartburn. Further, an inverse association demonstrated in esophageal biopsies between dilated epithelial intercellular spaces and baseline impedance in the distal esophagus, suggesting a physiologic correlation. Perhaps most striking was that, using a cutoff value of 2100 Ω, baseline impedance identified GERD patients with a positive and negative predictive value of 75% [57].

Figure 9.13 Novel MI balloon catheter with 36 channels measuring impedance axially and radially along a 10 cm length of the esophagus.

Source: Courtesy of Dr. David Katzka.

In addition, patients with hypersensitive esophagus have been shown to have significantly lower baseline impedance than healthy controls with similar acid exposure time. Furthermore, in one study of 48 GERD patients, median baseline impedance increased from 886 to 1372 Ω after PPI administration. In addition, baseline impedance was significantly lower in a cohort of 30 patients with PPI‐responsive functional heartburn compared with those without PPI response [58, 59]. In another study of heartburn patients, a baseline impedance value of 2446 Ω had a positive predictive value of 82% and a negative predictive value of 96% for identifying PPI‐responsive patients [60]. These studies suggest that baseline impedance in patients with functional heartburn and esophageal hypersensitivity may predict therapeutic outcomes. On the other hand, patients with Barrett’s esophagus have more permeable columnar mucosa and so low baseline impedance [61]. This was confirmed in a cohort of 10 patients after radiofrequency ablation in which baseline impedance was low before treatment but increased after squamous regeneration [62].